I'm using Pyrilutamide as monotherapy since 4 months. 0.5mg daily (Actifolic). I never had any side effect at all.
Just this week I compared pictures (I won't publish any, please don't ask for them) and made my self assessment and I think I have definitively lost density (I'm NW2). I will evaluate again at month 6 because I presume it can be a sheeding phase like with Finasteride. If that's the case, I should see positive changes by month 6. If not, well... I'll drop it and move on.
Good luck mates.